This is the most labor-intensive way to put references into EndNote, and the way that is most prone to errors. Use this method as a last resort, if you can't find your reference(s) in a database like MEDLINE, or in a library catalog like the National Library of Medicine for books or book chapters. (You would just need to get the record for the book and modify your EndNote record to reflect a chapter of that book).
The following video demonstrates how to manually enter records into your library in Endnote 20 for Windows. The steps are the same in Endnote 21 for iOS. Video does not have sound.